Immunosuppression

There are many factors that suppress both innate and acquired immunity levels but in pigs infectious agents are the most common ones. These include:

Mycoplasma hyopneumoniae the cause of enzootic pneumonia.

Pasteurella multocida.

Aujeszky's disease virus.

Swine influenza virus.

African swine fever virus.

PRRS virus.

These agents may destroy the macrophages or lymphocytes, or delay or reduce the efficiency of the immune response, or damage the innate defences.

Weaning time is also a period of immuno-suppression by withdrawal of the sows milk that contains the protective mechanisms of IgA. When pigs are mixed, moved or stressed the plasma cortisol levels rise with a similar effect and the demand for vitamin E rises.